Jefferson, named for Thomas Jefferson when it was founded in the early 1840s.
This is obviously not an original sign, because everybody knows there is no period abbreviating the "doctor" in Dr Pepper. Or, based on this Snopes page, it could just be a fresh coat of paint was applied to a pre-1950s ad:
Here's another oddball Pepper fact: The period after the "Dr" went missing in 1950 when the company changed the font used to write the name. When presented in this new style, the lower case "r" consisted of a small slanted line with a dot at its upper right. Well and good, but when a period was trailed after that new-fangled "r", the period and the r's dot seemed to form a colon and alter the "r" into an "i". With the period there, "Dr. Pepper" looked like "Di: Pepper". The solution was to drop the period.
I'd never seen one of these. This "traffic stop" was located right before the crosswalk at a stop sign. The date reveals it's from 1926. I guess it might have been effective with the motor vehicles of that era. "Cretney Traffic Guide Co, Madison, WIS" was the apparent manufacturer.